Appliance stabilized by a gyroscope, in particular a two-wheeled robot

ABSTRACT

Appliance such as a two-legged robot made up of a system giving ground support and an upper body ( 30 ), equipped with a gyroscopic rotor wheel ( 31 ) which acts as a fulcrum to balance the appliance when positioned in reverse pendulum. A satisfactory equilibrium is guaranteed, thereby releasing from this function the command system in charge of robot locomotion or pathway.

This invention relates to an appliance configured in reverse pendulum inrelation to gravity, stabilised by a gyroscope, such as a two-leggedrobot according to the application given chief consideration.

Mobile robots are of extremely different make-up depending upon theirmissions and the pathways along which they are likely to travel, but thechoice of a good solution raises problems in crowded environmentslittered with obstacles or with difficult access since the robot mustthen be provided with equilibrium, agility, flexibility and stabilityrelated properties so that it can make its way between obstacles,by-pass them or climb over them. Therefore tracked robots, some withseveral successive caterpillar axles, have been proposed. In oneappliance actually built, the front caterpillar axle was articulated tothe remainder of the robot so that it could be raised obliquely andassume the incline of stairs to be mounted: the caterpillar tracks ofthe front axle gripped several front treads at the same time enablingstair mounting to be initiated. But the drawback of caterpillar vehiclesis a relatively large requirement of ground space and difficulty inaccurate turning.

Robots mounted on feet or legs have also been put forward. Widelyvarying designs exist both in respect of the number of feet or legs andin respect of their properties, in particular concerning moving or shapechanging possibilities. One extreme construction is a one-legged jumpingrobot provided with a single foot; this foot is rigid but ends in a jackallowing its periodic extension and it is jointed to a robot body towhich it must give support. Sudden extension of the jack throws therobot body in the air and the piloting system adjusts the direction ofthe foot when it is lifted off the ground in order to prepare thefollowing jump and re-balance the robot or move it in the requireddirection. Produced prototypes show that this concept is perfectlyfeasible despite its lack of static stability. However robots aregenerally preferred which are equipped with a much higher number of feetand six-footed robots have in particular met with real popularity. Thesix feet are distributed into two groups of three which alternatelycarry out the same work: one of the groups of feet rests on the groundand maintains the robot body in equilibrium while the other group islifted and moved forward before being lowered to provide new support tothe robot ahead of the previous support, which enables the robot body tobe moved forward when the first group of feet is lifted. This is a verystable construction since the feet of each of the groups are arranged ina triangular base within which the centre of gravity of the robot isalways contained. But this stable equilibrium is obtained at the priceof the robot's complexity, large space requirement and relativelyconsiderable weight.

There is a temptation, however, to recall that artificial environmentssuch as factories, in which numerous robots need to move around, werefirstly designed for man, and to draw the conclusion that a robotimitating the form and walk of man as near as possible should give thebest results by offering a satisfactory compromise between complexrobots that are highly stable but voluminous and robots with a reducednumber of feet whose equilibrium raises problems. Experience has shownthat two-legged robots, made up of legs articulated independently fromthe robot body and fitted with a knee joint for alternate flexing andextension to imitate man's walk, require less space and can be of use indifficult, complicated situations by overcoming varied obstacles. Strictco-ordination however of the different motors controlling thearticulations is required to maintain equilibrium, and imitation -ofman's walk is less easy than may be thought.

The purpose of the invention is therefore to bring radical improvementto the stability of appliances having relatively unstable equilibrium,for example those configured in reverse pendulum such as one-legged,two-legged or even three-legged robots, since at certain times duringtheir movement they are only supported by two legs, by equipping themwith a gyroscopic rotor wheel located in an upper body supported by theleg or legs. The gyroscopic rotor wheel forms a “inertial fulcrum point”which, for an appliance whose static equilibrium is not assured, fulfilsthe same role as a balancing pole for a tightrope walker; the inventionalso comprises the automatism parts which make use of this fulcrum point(sensors or detectors, command system, actuators positioned between thebalancing pole and the tightrope walker to use the former image) inorder to balance the appliance in any position for a certain period oftime. In other words, the invention also enables stability to beimparted to the reverse pendulum appliance at any time, even if thesupporting leg is strongly inclined, provided however that certainoperating conditions are met.

This rotor wheel, intended to assure equilibrium, is to be distinguishedfrom the gyrometer of the robot in the article published by Matsumoto etal “A four-wheeled robot to pass over steps by changing running controlmodes” (IEEE International Conference, May 21, 1995, p. 1700 to 1706)which only serves to measure its tilt when in dynamic equilibrium and inno way contributes towards this equilibrium.

The operating conditions of the rotor wheel are related to theorientation of its spin axis, either relative to gravity or relative tothe mechanical suspension between the rotor wheel casing and the upperbody (for a one-legged appliance) or the intermediate body (for anappliance with at least two legs). These vary continually taking intoaccount that the spin axis of the rotor wheel drifts under the effect ofprecession. In particular, this drift limits the time interval in whichit is possible to immobilise the appliance in a position in which itssupporting leg is strongly inclined. It is possible to correct thiseffect by voluntary shifting of the whole appliance into a symmetricalconfiguration (or a series of configurations whose resultant issymmetrical) relative to the equilibrium configuration of the reversependulum, either by a strong tilt maintained for a short period of time,or by a less inclined tilt maintained for a longer time interval. It cantherefore be seen that the invention is particularly well adapted to thestabilisation of a walking two-legged robot which naturally alternatestilting.

The gyroscopic rotor wheel is placed in a casing, itself connected tothe upper body of the appliance by a mechanical suspension which allowsrotating movements about two nonparallel axes. This suspension with twononparallel axes is equipped with actuators able at any time to exert,between the rotor wheel casing and the upper body of the appliance, astabilising couple which opposes the off-balance effect produced bygravity on the appliance.

The command system adapted to the invention is able to measure the tilteffect produced by gravity on the appliance, to give a command foropposing action to the activators appropriate to achieve perfect balanceof the appliance, and to maintain this appliance within its operatingconditions. It is also able to co-operate with another command system,such as a system intended to command forward movement of the robot, thelatter system therefore being released of the function consisting ofseeking and maintaining equilibrium.

This task separation between the two command systems, one managing therobot's equilibrium and the other its forward movement, is an importantadvantage of the invention which makes co-operation between the systemseasy by doing away with the need for their coordination or strictsynchronisation. It sets itself well apart from the invention in thearticle “The walking gyro” (Robotics Age, vol. 7, No. 1, January 1985,pages 7 to 10, Peterborough, NH, USA) in which a gyroscopic rotor wheelundergoes tilting whose effect is to incline a rod in the form of abalancing pole at whose ends are fixed the feet of a two-legged robot:the rotor wheel serves to lift the feet alternately without referring toany other robot functions (such as equilibrium or walking).

To resume, the invention concerns an appliance made up of at least onesupporting leg and an upper body connected to the supporting leg, andconfigured in reverse pendulum relative to gravity, characterised inthat the upper body comprises a gyroscopic rotor wheel rotating around arotor axle and housed in a casing, the casing being connected to theupper body by a mechanical connection which permits rotational movementsabout two non-parallel axes, in that the appliance comprises sensorswith which the gravity-produced off-balance effect can be measured(moment of tilt), means able to equilibrate the appliance by exertingopposite forces to the imbalance (opposing moment) which use the supportof the gyroscopic rotor wheel by means of actuators, and in that itcomprises a command system able to take advantage of the actuators andsensors of the apparatus to assure its equilibrium at all times and evento co-operate with other command systems intended in particular tocontrol locomotion or pathway. One preferred embodiment consists ofmaking the mechanical connection adjustable between the rotor wheel andthe upper body by means of a Cardan suspension. In this case, the casingcontaining the rotor wheel is suspended from an inner suspension ring byan inner rotating suspension axle perpendicular to the rotation axle ofthe rotor wheel, and this inner ring is itself suspended from an outersuspension ring by an outer rotating suspension axle perpendicular tothe inner rotating suspension axle. The outer suspension ring isintegral with the upper body of the appliance to be balanced. The innerand outer suspension axes therefore form the effective mechanical axlesalong which suspension is built.

The invention may, advantageously, comprise several legs and form awalking two-legged robot which naturally alternates tilting. Accordingto one particular embodiment, it comprises two supporting legs jointedwith the upper body, each made up of two sections jointed together. Eachof these sections may comprise a foot, connected to the lower section bya joint having a vertical axis, fitted with a motor, which allowschanges of direction when walking. Said robot is able to be inequilibrium at all times, even when its centre of gravity is off-centrein relation to its base, such as for example during the phase of walkingwhen it is strongly inclined and on the point of placing its second footon the ground.

Advantageously, the off-balance effect due to gravity on the appliancemay be measured by two tiltmeters or two sensors of angular velocityplaced along orthogonal axes, either on the leg for a one-legged robotor on one connecting section for a two-legged robot.

For walking robots, the command system may make use of the alternatemoments of tilt by seeking to make their average over a time periodvirtually zero or, which amounts to the same thing, to make the averageof compensating opposing moments virtually zero.

The invention may advantageously comprise means with which it ispossible to measure the orientation of the spin axis of the rotor wheel,in order to monitor the operating conditions of the appliance takinginto account that the spin axis of the rotor wheel drifts under theeffect of precession. One simple means of measuring this orientationconsists of placing angle position sensors on the mechanical suspensionaxles and to connect these to a specific part of the command system.

The invention is described below with the aid of the following Figures:

FIG. 1 is a view of a gyroscopic rotor wheel according to the invention,

FIG. 2 is a view of a one-legged appliance stabilised by a gyroscope inaccordance with the invention

FIG. 3 is a view of a two-legged robot stabilised by a gyroscope inaccordance with the invention,

FIG. 4 is a diagram of a command system of the robot in accordance withthe invention.

FIG. 1 shows a rotor wheel enclosed in a casing 1 and which essentiallycomprises a part made up of an inertia wheel 2 and a wheel rim 3; arotor axle 4 is joined to wheel rim 3 and rotates at high speed in apair of bearings 5 and 6, generally magnetic bearings or having notangible contact in order to eliminate friction. Casing 1 is placed in avacuum for the same purpose. Rotor axle 4 is lined with an armature 7able to be driven by a coil 8 of an electric motor in order to set inmotion the gyroscopic rotor wheel at the start of a mission. Once inmotion, the rotor wheel may also form a storage means in mechanical formfor the energy required by the appliance during its mission. For thispurpose, it is recommended to use a reversible electric motor, that isto say one which is also able to function as a generator by collectingin coil 8 a current induced by the free rotation of armature 7. Suchreversible motors are known in the art and will therefore not be furtherdescribed herein.

FIG. 2 shows a particular embodiment in which the system of FIG. 1 andthe sensors, actuators and command system in accordance with theinvention are incorporated in the body of an appliance to be balanced.For illustration purposes casing 1 is symbolised by a plain box androtor axle 4 is represented by an axis. Casing 1 is suspended from aninner ring 9 surrounding it, via an inner suspension axle 10perpendicular to rotor axle 4; in similar manner, inner ring 9 issuspended from an outer ring 11 via an outer suspension axle 12 orientedperpendicular to the inner suspension axle 10. Outer ring 11 is part ofthe outer structure of the body of the appliance and may for examplerest on the ground by means of a single foot 13. The rotor wheel made upof the inertia wheel 2 and wheel rim 3 is therefore a gyroscopic rotorwheel whose rotor axle 4 may move in any direction by means ofappropriate rotations of suspension axles 10 and 12.

If the system is caused to maintain the configuration of FIG. 2, withthe exception of the rotor wheel which remains free to rotate aroundrotor axle 4, by blocking suspension axles 10 and 12, the applianceremains in dynamic equilibrium on foot 13 and makes an orbitalprecession movement during which rotor axle 4 makes a conical rotationwhose central axis is the vertical 14 passing through fulcrum point 15of foot 13 on the ground. Precession velocity is fairly slow in practiceand could therefore be acceptable for numerous applications. Germanpatent 42 11 423 describes a two-legged robot equipped with such agyroscopic rotor wheel whose rotor axle is fixed to the robot's body andtherefore assures such dynamic equilibrium, but the precession movement,which is accompanied by lifting and lowering movements of the legs, mustgreatly complicate walking and the long-term maintaining of equilibriumis unsure.

We have chosen not to satisfy ourselves with this situation but have setout to temporarily immobilise the body of the appliance (comprising inparticular outer ring 11 and foot 13). Suspension axles 10 and 12 areequipped for this purpose with motors 16 and 17 respectively which carryrings 9 and 11. If it is reasoned in terms of equilibrium of forces, itcan be ascertained that the appliance is subject to a moment of tiltthat it equivalent to the product of its weight (P=Mg) and the length ofthe horizontal projection between the ground support point 15 and thecentre of gravity of the system. Motors 16 and 17 are then caused tosubmit suspension axles 10 and 12 to moments whose product is anopposing moment which balances out this moment of tilt. Since thismoment of tilt changes over time, command of the opposing moment must begenerated by a servo-control loop.

To measure the tilt effect, it is possible in practice to positiongyrometers 18 and 19, or tilt meters, orthogonal fashion on foot 13.Measurements of tilt velocity are transmitted to servo-control loops 20and 21 which respectively command motors 16 and 17.

Equilibrium is temporarily achieved for zero set velocities given to theservo-control loops, that is to say when the tilt velocity measured bygyrometers 18 and 19 is an average of zero for a relatively short timeinterval; otherwise a non-zero set velocity is applied to upright thebody of the appliance.

FIG. 3 shows another particular embodiment in which the system of FIG. 1and the sensors, actuators and command system according to the inventionare incorporated in a two-legged robot. It comprises an upper body 30equipped with a gyroscopic rotor wheel assembly 31 meeting thedescription of FIGS. 1 and 2, other than that foot 13 resting on theground is omitted in this case. It is replaced by a connecting section32 (carrying gyrometers 18 and 19 which are not shown) and to which thetwo legs 33 (respectively 33 d for the right leg and 33 g for the leftleg) of the robot are jointed by a hip joint 34 (respectively 34 d forthe right leg and 34 g for the left leg). Legs 33 are made up of anupper section 35 and a lower section 36 jointed together by a knee joint37 to reproduce the essential parts of the human leg; lower section 36is fitted with a foot 38 which may be circular and with a very smallsurface area owing to the favourable balance-maintaining properties ofthe gyroscope system which advantageously distinguishes the inventionfrom other two-legged robots provided with large rectangular feet toguarantee equilibrium at all times.

Walking movement is controlled in extremely simple fashion: the robotremains supported by one leg 33 while the other leg moves forward tomake a step. Extension of the front leg and flexion of the hind legallow transfer of body weight of the robot 30 from one leg to the otheras in human walking. Stabilisation control over the body of the robot 30by the rotor wheel is commanded by command system 45 and servo controlloops 20 and 21, independently from command of the forward movement ofthe robot or its pathway which is assured by another command system thatis independent but with which the system of the invention co-operates.This results from the equilibrium of the robot at all intermediate timesbetween two steps, contrary to the prior art in which temporaryimbalance interfered with the locomotion or pathway command.

This equilibrium imparts particular advantage to a process for causingthe robot to turn by means of a vertical axis joint 41, connecting eachof feet 38 to the associated lower section 36, and equipped with a motor42 which is set in motion when the leg under consideration rests on theground.

Advantageously, the energy required for the different motors andautomatism parts on board is taken from the rotating energy of the rotorwheel and the robot does not carry any source of energy. By choosing amotor of reversible type, it is possible to use the voltage at theterminals of coil 8 provided that an adjuster and distributor box isused for this energy. The kinetic energy of the rotor wheel thereforegradually converts into electric energy. The quantity of energy it ispossible to accumulate in a gyroscopic rotor wheel is sufficient for thetwo-legged robot to be able to achieve concrete missions; if the case istaken of a rotor wheel in carbon fibre, a material chosen for the hightangential velocity v=ωr to which it can be submitted (v greater thanapproximately 800 m/s); angular velocity ω may exceed ω=8000 rd/s, andfor a radius of r=0.10 m in which the material of the rotor wheel isconcentrated, the kinetic moment H=mr² ω will be greater than 80 Nms fora rotor wheel with a mass of 1 kg. However the kinetic moment of a rotorwheel may be interpreted as the product of a couple reserve C availablefor a time t. It is therefore possible to apply relatively high couples,sufficient to stabilise a lightweight robot or set it upright after afall.

FIG. 4 is a diagram of a command system of the robot in accordance withthe invention. Before each mission, the gyroscopic rotor wheel isaccelerated by supplying the reversible motor from an outside directcurrent source, then the robot is released. In this diagram most of theactive parts of the robot are shown in particular the casing of thegyroscopic rotor wheel, actuators 16 and 17 which in this case areelectric motors, and gyrometers 18 and 19.

The elements of command 45 comprise in particular a balancing system 46which gives a set signal to servo-control loops 20 and 21 according tothe description in FIG. 2. These loops provide current to reversiblemotors 16 and 17 from a current produced by conversion of the kineticenergy of the gyroscopic rotor wheel.

According to one preferred embodiment, angle position sensors 47 and 48which measure the angle position of inner suspension axle 10 and outersuspension axle 12 are used to monitor the operating conditions of theappliance taking into account that the spin axis of the rotor wheeldrifts under precession. These angle position sensors are connected to aspecific part of the command system called a monitoring system 49 whichis also in charge of commanding voluntary shifting of the applianceassembly into a symmetrical configuration relative to the equilibriumconfiguration of reverse pendulum, in order to generate by precession adrift that is opposite to the spin axis of the rotor wheel.

Finally, this monitoring system 49 is able to cooperate with one or morecommand systems 50, in charge for example of commanding the locomotionor pathway of the appliance, such as to release these other commandsystems from all the functions required for seeking and maintainingequilibrium, and from all functions required for maintaining theinvention within its operating conditions.

FIG. 4 also shows other parts of the robot which are not directlyrelated to the invention, namely an energy pack box 51 connected to coil8 and to the command and activating systems to supply them with energyin a form appropriate to them, an angular velocity sensor 52 measuringthe velocity of axle 4 to check that it is sufficient, servo-controlloops 53 for positioning of legs 33, controlled by one of the othercommand systems 50, commanding motors 39, 40, 42 corresponding to joints34, 37, 41. These joints, present on each leg right and left, are fittedwith sensors (not shown) to bring them into required positions. Finally,it has been seen that the monitoring system 46 can be divided into amanagement system for voluntary tilting 55 intended to upright the robotand a forbidden configuration avoidance system 56 which prohibits thegyroscopic rotor wheel from reaching positions in which it could nolonger serve as an inertial fulcrum point.

A further possible application of the invention, different from a mobilerobot, consists of dynamic scaffolding to conduct repair or inspectionwork at heights. It is simply required to fit the system in FIG. 2 witha tool or desired equipment connected to the body of the appliance, andto allow it to upright itself on foot 13, which may be jointed ortelescopic, when the rotor wheel has been charged with kinetic energy.It suffices to set in motion servo-control loops 20 and 21 in FIG. 2 tostabilise the scaffolding. At the end of the mission, the foot isretracted or the appliance placed against a wall before the rotor wheelstops.

What is claimed is:
 1. Appliance comprising at least one supporting leg(13, 33) and an upper body (11, 30) connected to the supporting leg, andconfigured in reverse pendulum relative to gravity, in which the upperbody comprises a gyroscopic rotor wheel (2, 3) rotating about a rotoraxle (4) and housed in a casing (1), characterized in that the casing isconnected to the upper body by a mechanical connection which permitsrotational movements about two non-parallel axes, the appliancecomprises two sensors (18, 19) disposed in an orthogonal fashion aroundthe appliance, for the measurement of an off-balance effect produced bygravity on the appliance, and means to balance the appliance by exertingopposing forces opposing the off-balance effect, which comprise: twoactuators (16, 17), for imparting the rotational movements about the twonon-parallel axes to the casing (1) and the gyroscopic rotor wheel; anda command system to which measurements by the sensors are transmittedand which commands the actuators.
 2. The appliance according to claim 1,characterized in that the mechanical connection which permits rotationalmovement about two non-parallel axes comprises a carden suspension, suchthat by suspending the casing (1) from an inner suspension ring (9) bymeans of an inner rotating suspension axle (10) perpendicular to therotor axle (4), and by suspending the inner ring from an outersuspension ring (11) by means of an outer rotating suspension axle (12)perpendicular to the rotor axle (4).
 3. The appliance according to claim1, wherein the appliance is a two-legged, walking robot, furtherincluding two supporting legs (33) jointed with the upper body (30)wherein each of said two supporting legs are formed of two sections (35,36) jointed together the legs further including feet disposed oppositethe main body.
 4. The appliance according to claim 1, characterized inthat an off-balance effect produced by gravity on the appliance ismeasured by gyrometers (18, 19) to measure tilt velocity, or tiltmeters, wherein the command system (45) is sensitive to the measurementsof these gyrometers or tilt meters and causes opposing moments dependenton tilt velocity to be applied via actuators (16, 17).
 5. The applianceaccording to claim 1, characterized in that it comprises means (47, 48)for measuring the orientation of the casing of the rotor wheel relativeto the upper body or to a connecting section (32) of the appliance. 6.The appliance according to claim 1, characterized in that the commandsystem uses information from the means (47, 48), for measuring theorientation of the casing of the rotor axle (4) of the rotor wheelrelative to the upper body of the appliance to maintain the appliance inan operating condition.
 7. The appliance according to claim 1,characterized in that the command system is also able to co-operate withone or more command systems (50, 53), in charge of commanding travelmovements of the appliance.
 8. The appliance according to claim 1,wherein the appliance is a two-legged robot.
 9. The appliance accordingto claim 2, wherein the appliance is a two-legged robot.
 10. Theappliance according to claim 3, wherein the appliance is a two-leggedrobot.
 11. The appliance according to claim 4, wherein the appliance isa two-legged robot.
 12. The appliance according to claim 5, wherein theappliance is a two-legged robot.
 13. The appliance according to claim 6,wherein the appliance is a two-legged robot.
 14. The appliance accordingto claim 7, wherein the appliance is a two-legged robot.
 15. Appliancecomprising at least one supporting leg (13, 33) and an upper body (11,30) connected to the supporting leg, and configured in reverse pendulumrelative to gravity, in which the upper body comprises a gyroscopicrotor wheel (2, 3) rotating about a rotor axle (4) and housed in acasing (1), characterized in that the casing is connected to the upperbody by a mechanical connection which permits rotational movements abouttwo non-parallel axes, the appliance comprises two sensors (18, 19), forthe measurement of an off-balance effect produced by gravity on theappliance, and means to balance the appliance by exerting opposingforces using the support of the gyroscopic rotor wheel via actuators(16, 17), and an associated command system able to take advantage of theactuators and sensors of the appliance to give it equilibrium,characterized in that an off-balance effect produced by gravity on theappliance is measured by gyrometers (18, 19) to measure tilt velocity,or tilt meters, wherein the command system (45) is sensitive to themeasurements of these gyrometers or tilt meters and causes opposingmoments dependent on tilt velocity to be applied via actuators (16, 17),wherein the command system comprises means for calculating the timeaverage of moments of tilt, connected to servo-control means (20,21) forthe actuators, calculating the opposing moments to have applied by theactuators such that the moments of tilt have a zero time average. 16.The appliance according to claim 15, wherein the appliance is atwo-legged robot.
 17. Appliance comprising at least one supporting leg(13, 33) and an upper body (11, 30) connected to the supporting leg, andconfigured in reverse pendulum relative to gravity, in which the upperbody comprises a gyroscopic rotor wheel (2, 3) rotating about a rotoraxle (4) and housed in a casing (1), characterized in that the casing isconnected to the upper body by a mechanical connection which permitsrotational movements about two non-parallel axes, the appliancecomprises two sensors (18, 19) for the measurement of an off-balanceeffect produced by gravity on the appliance, and means to balance theappliance by exerting opposing forces using the support of thegyroscopic rotor wheel via actuators (16, 17), and an associated commandsystem able to take advantage of the actuators and sensors of theappliance to give it equilibrium, wherein the gyroscopic rotor wheel (2,3) is a sole source of energy for the appliance, and wherein saidgyroscopic rotor wheel is driven by a reversible motor (7, 8) furtherable to operate as electricity generator.
 18. The appliance according toclaim 17, wherein the appliance is a two-legged robot.
 19. Appliancecomprising at least one supporting leg (13, 33) and an upper body (11,30) connected to the supporting leg, and configured in reverse pendulumrelative to gravity, in which the upper body comprises a gyroscopicrotor wheel (2, 3) rotating about a rotor axle (4) and housed in acasing (1), characterized in that the casing is connected to the upperbody by a mechanical connection which permits rotational movements abouttwo non-parallel axes, the appliance comprises two sensors (18, 19) forthe measurement of an off-balance effect produced by gravity on theappliance, and means to balance the appliance by exerting opposingforces using the support of the gyroscopic rotor wheel via actuators(16, 17), and an associated command system able to take advantage of theactuators and sensors of the appliance to give it equilibrium, whereinthe gyroscopic rotor wheel (2, 3) is housed in a vacuum casing (1), andwherein the rotor axle (4) is supported by bearings.
 20. The applianceaccording to claim 19, wherein the appliance is a two-legged robot.